Thin sheet materials, such as glass plates, glass-ceramic plates, ceramic plates and crystalline wafers, and the like, are used widely in many processes and devices. Each piece of sheet material typically comprises at least two major, opposing surfaces joined by edge surfaces. During the manufacture, handling, transpiration and use of these sheet materials, they are subjected to contact with other sheet materials, equipment, tools and accordingly the impact of various external forces. Frequently, the mechanically weakest parts of the sheet material are the edge surfaces and the peripheral regions of the major surfaces. Without protection of these weak areas, the sheet material are prone to failure such as chipping, cracking and even rupture when the external force exceeds a certain limit.
Such is especially the case for glass sheet materials, especially thin glass sheets having a thickness of less than 1 mm, in certain embodiments at most 500 μm, in certain embodiments at most 300 μm, which have found extensive use in making display devices, e.g., as TFT and color filter substrates in liquid crystal displays (LCDs), organic light-emitting diode (OLED) display substrates, display cover sheets, and the like. These glass materials tend to have high surface quality, especially those made by using the overflow down-draw process, a technology pioneered by Corning Incorporated, Corning, N.Y., U.S.A. However, due to the cutting and edge finishing processes these glass sheets have to undergo, mechanical defects are not completely avoidable on the edge surfaces and in the peripheral regions of the main surfaces. Edge protection via encapsulation by using a relatively soft material was found especially conducive to reduced product cracking and other failure for thin glass sheets products.
A particularly interesting ultra-thin glass sheet product is in the form of a spool, in which a long thin glass ribbon, such as one having a thickness of 100 μm or even lower, is wound onto a mandrel to form a roll. The roll of glass ribbon may be unrolled into flat shape, subjected to surface processing such as coating deposition, semiconductor device formation, and the like, and then re-wound into a roll. This roll-to-roll process can be particularly advantageous for making various opto-electronic devices such as e-ink-based displays, photovoltaics, and the like. However, in a glass sheet roll, the glass ribbon is subjected to compressive stress on one side, and tensile stress on the other. Any edge defect or edge impact can easily lead to chipping and/or breakage. Thus, edge protection is particularly important for such glass spool.
US Patent Application Publication No. 2011/0023548A1 discloses an edge-protected glass sheet product, in which the edge surface and the peripheral regions of the main surface of the glass sheet are protected by a continuous web material such as polyimide and the like bonded to the peripheral regions. It is disclosed in this reference that the edge protection web can be used for protecting the edges of a spooled glass ribbon. While the continuous web material provides adequate protection to the glass sheet, it poses technical challenges during subsequent finishing step when the glass sheet or ribbon is cut into multiple pieces, and when the web material is removed. It was found that mechanical cutting of the web material can be difficult to align with the separation line of the glass sheet. In the case of laser cutting by using a CO2 laser beam, which is advantageously used for cutting thin glass sheets, exposure of the organic web material in air to the laser beam can lead to combustion, toxic fume formation, and charring of the glass surface.
Thus, there remains a genuine need of an edge-protected product that does not have the above issues.
The present invention satisfies this and other needs.